John david and carl le doux



NITED STATES PATENT OFFICE.

JOHN DAVID AND CARL LE DOUX, OF LONDON, ENGLAND, ASSIGNORS TO HENRYERNEST FRY, OF SAME PLACE.

PROCESS OF SMELTlNG LEAD ORE.

SPECIFICATION forming part of Letters Patent No. 559,935, dated May 12,1896.

Application filed October 11, 1895. Serial No. 565,392. (No specimens.)

1'0 aZZ whom, it may concern.-

lle it known that we, JOHN DAVID an d CARL LE DoUX, chemists, subjectsof the Queen of Great Britain, residing at 28 Billiter Buildings,Billiter Street, in the city of London, ingland, have invented certainnew and useful improvements in the extraction of lead, with silver,gold, or other metals, from galena or sulfids of lead and zinc and frommattes or refractory ores, of which the following is a specification.

This invention relates more especially to the treatment of thosesulfuret ores of lead which also contain zinc. Such ores, especiallywhen the proportion of zinc is at all considerable, are very refractoryand diflicult to deal with. In the ordinary way ores of this class canonly be advantageously treated by mixing them with other ores, so thatthey form but a small part of the bulk; otherwise in the smelting thelosses both of lead and the precious metals, which such ores frequentlycontain, become excessive.

By this invention sulfuret ores of lead may be smelted without undueloss even when they contain large quantities of zinc. This is effectedby the use of a special flux prepared from sulfate of soda, which isobtainable in the form of niter-cake or salt-cake and oxid of iron,which may be in the form of burnt pyrites. Sulfate of potash in lieu ofsulfate of soda might in like manner be employed, excepting that itsgreater cost g enerallyprohibits its use. The ferruginous matter mayalso be in other form.

In the preparation of the flux it is preferred to proceed as follows: Acharge of niter-cake or sulfate of soda in other form is fused on thebed of a reverberatory furnace, and to it is gradually added,withconstant stirring, half its weight of burnt pyrites in a finely-dividedstate. The whole is worked together until complete mixture is obtained,and then the fluid flux so formed is run out of the furnace and allowedto cool. Afterward the flux is broken up into small lumps ready for use.

The furnace-bed is preferably formed of basic bricks.

The reactions which occur in the prepara tion of the flux frommiter-cake in the manner above described may be represented by formulm,as follows:

Commercial m ter-cake. ZZNaHSO +XH SO +XH O Sodium ferra'e. Na SO +Fe O=Na Fc O,+SO \Vhen this flux is employed in the smelting operation, itcombines with the zinc contained in the charge and forms with it aliquid slag. It is this property which renders it particularly valuablein the smelting of refractory lead ores.

The lead ore is preferably treated in the following manner: It isprepared by breaking it small, so that it will pass through a sievehating, say, eight holes to the linear inch. The ore thus pulverized isthen roasted at a moderate heat in a reverberatory furnace, on the bedof which it is spread in a layer about four inches deep. \Vhile it isroasting, the ore is constantly turned over with paddles and exposed tothe air until sulfurous fumes cease to be evolved. This operation willusually extend over many hours. When the ore is ready, it is graduallybrought with the paddles up toward the fire end of the furnace, wherethe heat will cause the ore to cohere sufficiently to admit of its beingmade up into small ballssay from two to four inches in diameter. In thisstate the roasted ore is withdrawn from the furnace and allowed to cool.The smelting may be performed in a cupola-furnace. The furnace ischarged with a mixture composed, preferably, of the prepared ore, theflux already described, some slag from a previous operation, and also,if readily obtainable, a proportion of a freelymelting slag from someother metallurgical operation, such as the smelting of iron or copper.Together with these materials the furnace is fed with fuel in sufficientquantity to melt the charge. The proportion of ore to the otheringredients of the charge should vary with the nature of the ore undertreatment. Usually for one hundred parts of an average ore of this classit will be suitable to employ from ten to twenty-five parts of flux andfrom twenty-five to eighty parts of slag from a previous operation and,say, ten parts of some other freely-melting slag. The object to beattained is that in the smelting operation the Zinc contained in thecharge should combine with the flux and pass into slag, and that theresulting slag should be sufficiently fluid to flow freely. The flux isto be used in sufficient quantity to attain both these ends. In otherrespects the smelting operation is performed in the ordinary manner. Thelead is collected in a pot, in which it is allowed to stand in a meltedstate. Sometimes a little matte separates from the metal. It forms alayer on the surface of the molten lead. The matte, when so formed,consists for the most part of sulfids of iron and sodium, together witha little lead. It is carefully collected, and after a few days whenexposed to the atmosphere it disintegrates and falls into powder. Thispowder is roasted, so as toreduce the sulfids it contains, and it ispassed again through the smelting-furnace, where it replaces an equalquantity of flux. The lead is treated in the usual way to recover anysilver and precious metals which it may contain.

The changes and reactions taking place in the cupola are probably asfollows: The lead is precipitated from its compounds by the oxids ofiron, while the zinc compounds are fluxed by the sodium sulfid and ironsulfid which are respectively formed by the reduction of the sulfate ofsoda by the carbon used as fuel, Na SO,+4EC: Ta S-HO0, and by the sulfurtaken up by the iron from the sulfurbearing constituents of the oree.1.,

The sulfid of sodium has the wellknown property of forming very easilyfusible compounds with other metallic suliids. It is impossible to givewith absolute certainty the exact formulae for such complex sulfids. Thefollowing may be existent:

Na S Feu ZnS analogous with the Na S QFeS.

These compounds would be found entirely in the slags as such were it notfor the silicic acid contained in the ore and burned pyrites used. Atthe smelting-zone the silica has the property of driving oif otheracids, including the hydrosulfuric acid, and this accounts for thepresence of some silicates of zinc, iron, and soda in the resultantslags.

Having now particularly described and ascertained the nature of our saidinvention and in what manner the same is to be performed, we declarethat what we claim is 1. The herein-described process of smelting leadores, with a flux prepared with sulfate of soda and iron oxid.

2. The herein-described process of smelting lead ores with a fluxprepared with nitcr-calce and burned pyrites.

3. The flux herein described formed from niter-cake and burned pyrites.

JOHN DAVID. CARL LE DOUX. \Vitnesses:

XVILLIAM Cox, H. J. HAYES.

